You need to ensure that outdated DNS records are automatically removed from the DNS zone

You have a single Active Directory domain.
All domain controllers run Windows Server 2008 and are configured as DNS servers.
The domain contains one Active Directory-integrated DNS zone.
You need to ensure that outdated DNS records are automatically removed from the DNS zone.
What should you do?

A.
From the properties of the zone, modify the TTL of the SOA record.

B.
From the properties of the zone, enable scavenging.

C.
From the command prompt, run ipconfig /flushdns.

D.
From the properties of the zone, disable dynamic updates.

Explanation:
Answer.From the properties of the zone, enable scavenging.
http://technet.microsoft.com/en-us/library/cc753217.aspx
Set Aging and Scavenging Properties for the DNS Server
The DNS Server service supports aging and scavenging features. These features are provided as a
mechanism for performing cleanup and removal of stale resource records, which can accumulate in zone data
over time. You can use this procedure to set the default aging and scavenging properties for the zoneson a
server.
Further information:
http://technet.microsoft.com/en-us/library/cc771677.aspx
Understanding Aging and Scavenging